1. Field of the Invention
This invention related to a tape carrier for a liquid crystal display (LCD) driver package and an LCD using such a tape carrier.
2. Related Art
A liquid crystal display (LCD) uses 9 TAB tape carrier as a means of connecting its printed circuit board to the electrodes on the glass board of its liquid crystal panel. An LCD driver chip is mounted on the TAB tape carrier. FIG. 1 shows a conventional TAB tape carrier 10 for an LCD driver package. FIG. 2 shows the state in which such a tape carrier is connected to a printed circuit board and the glass board of a liquid crystal panel. The TAB tape carrier 10 has an insulating film tape 11 formed of a polyimide layer, input lead conductors 12 laid on its surface, and output lead conductors 14. The TAB tape carrier 10 has a chip mounting opening 16, which provides a chip mounting site. The input leads 12 extend from the chip mounting opening 16 toward one edge of the tape and are terminated across a long slot 18 formed along this edge. The output leads 14 extend from the chip mounting opening 16 toward the other edge of the tape. On the side of the output leads 14, no opening is formed. An LCD driver chip 22 is connected to the input leads 12 and output leads 14 in the position of the chip mounting opening 16. In this manner, an LCD driver tape carrier package is formed.
When an LCD driver package is mounted on an LCD unit, the tape edge on the side of the input leads 12 is cut along line A--A (FIG. 1), so that the tips of the input leads 12 are exposed. The exposed tips of the input leads 12 are soldered to the corresponding conductors (not illustrated) of the printed circuit board 24 and the output leads 14 are connected to the corresponding panel electrodes of the LCD glass board 26. Since the output leads 14 are usually formed at a higher density than the input leads 12, they are liable to cause problems such as short-circuiting when connected, if the output leads 14 are not backed with the film tape. For this reason, the output leads 14 are connected to the glass board in a state of being supported on the insulating film tape 11. Since the glass board is flat, the output leads 14 can be connected even as they are attached to the insulating film tape 11. On the other hand, the conductors on the printed circuit board 24 are not necessarily of equal height and hence the input leads 12 are exposed so that they can adapt to such differences in height.
In the conventional structure, the tape 10 suffers repetitive stress in the directions indicated by arrows 28 and 30 on account of the difference in thermal expansion coefficient between the printed circuit board 24 and the LCD glass board 26 as well as vibration, or deflection or deformation of the printed circuit board 24. The stress in the tape 10 causes twists or wrinkles chiefly in regions 32 and 34, and thus inflicts damage particularly on the input leads 12 near regions 36 and 38 with a high probability of lead breaking. The output leads 14 are relatively high in mechanical strength because of being supported by the insulating film tape 11 and hence hardly suffer any damage. It is advantageous to shorten the length, L (FIG. 2), of the TAB tape carrier 10 for making the LCD driver assembly compact, and to widen the width, W, according to enlarging of the display. However, as the length, L, of the TAB tape carrier 10 becomes smaller and the width, W, becomes greater, the tape carrier 10 becomes more susceptible to damage by stress.
As conventional measures for solving this problem, there are known some methods: (1) reinforcing the input leads by resin coating, (2) providing dummy leads on both sides of the input lead array, or (3) thickening the lead conductors. However, the method of resin coating involves some problems. That is, silicone resin is used in the method for curing temperature requirements, but silicone resin does not ensure sufficient strength. It entails a troublesome resin coating step, and, in addition, makes it impossible to replace the driver package after resin coating. The method of providing dummy leads can prevent leads adjacent to such dummy leads from being damaged, but cannot prevent leads remote from the dummy leads from being damaged. The method of thickening leads is not economical and also makes fine patterning difficult.